Chelsea, last season's Champions League winners, were demoted to the Europa League after failing to advance from the group stages of Europe's premier club competition.
"Like every footballer, I've dreamt of playing in a game like this against such a big club - I just couldn't imagine it would come so soon," Krejci told UEFA's website.
The 20-year-old, who scored his first goal for the Czech Republic in his second appearance last week, has vowed not to be fazed.
"I feel respect towards the big names, but that will be gone once the referees first blows his whistle," he added. "We will fully concentrate on our performance."
Sparta's form is uncertain. It will be their first competitive fixture since December 6, when they met Atletico Madrid in the Europa League group stages due to the winter break.
The hosts are confident though, having last lost a European fixture at their Generali Arena home against MSK Zilina in the 2010/11 Europa League play-offs.
"Our coach [Vitezslav Lavicka] keeps reminding us that we're preparing for a big game," Krejci added.
"This has helped our motivation in training, as we've known we've had to take that extra step or run even faster.
"Everybody is taking this match as a reward for our performances in the group stage.
"It is a tremendous match, but that doesn't mean we don't want to get a good result."